Leak proof bottom for a paperboard container

ABSTRACT

Disclosed is an improved bottom closure for a paperboard container of the type commonly used to package milk. The improvement specifically relates to the blank from which the container is formed. When a container is formed from a blank which embodies this improvement, leaks in the bottom closure thereof are substantially prevented.

United States Patent Brownlee et a1. Oct. 21, 1975 LEAK PROOF BOTTOM FORA 2,496,043 1/1950 Farrell 229/31 ux PAPERBOARD CONTAlNER 2,926,7773/1960 Maguire 229/37 R X 3,120,335 2/1964 Egleston et a1. 229/17 G 1Inventors: Milton Brownlee. Mobile, A a". 3,194,473 7/1965 Rumberger229/31 x Thomas A. Tomlin, isle of Palms, 3,365,111 1/1968 McNair et a1229/17 0 S.C. 3,412,922 11/1968 Miller et al. 229/17 G X 3,421,6781/1969 Thompson et a1. 229/31 [73] Assigneez lnternatlonal PaperCompany, New 3,455,496 7H969 Franz York, 3,474,951 10/1969 Egleston etal. 229/17 0 x 22 Fil d: l 12, 1973 I l c J y Primary Examiner.lohn W.Huckert 1 1 pp 373,535 Assistant ExaminerStuart S. Levy Attorney, Agent,or FirmAlfred L. Michaelsen 52 [1.8. CI. 229/38- 229/31; 229/43; l229,43 T 57 ABSTRACT [51] Int. C19,... B651) 5/08; B65D 5/40; B65D 5/62Disclosed is an improved bottom closure for a paper- [58] Field ofSearch 229/11, 17 G, 37 R, 38, board container of the yp monly used opack- 229/43, 44 R, 43 SC, 43 T age milk. The improvement specificallyrelates to the blank from which the container is formed. When a [56]References Cited container is formed from a blank which embodies thisUNITED STATES PATENTS improvement, leaks in the bottom closure thereofare 2,362,862 11/1944 Sidebotham 229/48 T x substamally Prevented2,440,664 4/1948 lrons 229/48 T X 11 Claims, 8 Drawing Figures US.Patent Oct. 21, 1975 Sheet 1 of4 MKA US. Patent Oct. 21, 1975 Sheet3of43,913,826

U.S. Patent Oct.21, 1975 Sheet4 of4 3,913,826

LEAK PROOF BOTTOM FOR A PAPERBOARD CONTAINER BACKGROUND OF THEINVENTION 1. Field to Which the Invention Pertains This inventionpertains to the fluid packaging art.

A substantial quantity of fluids are packaged in paperboard containerswhich have been coated with a thermoplastic, e.g. polyethylene.Quantitatively, the major proportion of containers of this type are usedfor packaging milk. With respect to milk containers, the containerconstruction which is predominantly used is a so-called gable topcontainer which is formed from a one piece blank.

By way of background, milk carton blanks are typically manufactured bypaper companies. More particularly, paperboard of the desired basisweight (pounds per 3 thousand square feet) is continuously manufacturedon a paper machine and stored in large rolls. Subsequently, thepaperboard thus manufactured is unrolled and fed through an extruderwherein polyethyl ene is extruded onto the surfaces of the paperboard toprovide a coating. Thereafter, the thermoplastic coated paperboard isgenerally rerolled. The coated paperboard is fed into a press which cutsthe continuous web of paperboard into container blanks of the desiredsize. Additionally, the same press may be employed to provideappropriate score lines which facilitate the folding and erecting of thecontainer as well as any printing or art work. Thus, the productresulting at this point is a flat, thermoplastic coated paperboard blankwhich has been appropriately cut and scored. Generally, at this point,the two longitudinal edges of the blank are joined so as to form asquare tube. Commonly, the joining of the two longitudinal edges isachieved through a heat seal, i.e. the polyethylene coating adjacent tothe two longitudinal edges is heated and the two heated edges arepressed together. Tubes of the type thus formed are generally sold in aflat condition, by the manufacturing company, to a dairy.

When received by the dairy, the paperboard tubes are usuallysequentially fed into a so-called form, fill and seal machine.Typically, in such a manner, the paperboard tube which was shipped in aflat condition is formed into a square tube and deposited upon anupstanding, square mandrel. The tube is placed on the mandrel so thatthe part of the tube which will form the bottom of the container extendspast the exposed end of the mandrel. Thereafter, the machine proceeds toposition the carton under a heater which heats the polyethylene coatingon the bottom forming flaps to a temperature at which the polyethylenecoating will act as a bonding or adhesive agent. The machine thenproceeds to manipulate the flaps extending past the end of the mandrelso as to form a bottom closure. When a bottom closure has beenappropriately formed by juxtaposing the integral flaps on the tube, themandrel moves such that the formed bottom is pressed against a series ofcooled plates (pressure pads) for a time sufficient to effect a heatseal between the bottom forming flaps. Thereafter, the open topcontainer thus fomted is stripped off the mandrel, filled with milk andthe top is appropriately sealed. For the purpose of describing theinstant invention, the process steps of filling the container andsealing the top thereof are not particularly significant because theinstant invention relates to an improved, bottom closure.

What is of significance and what is thought to be apparent from theabove description is the fact that, gen erally, the blanks used to formsuch containers are manufactured by paper companies while the blanks areformed into containers by dairies using large, expensive equipment whichis located at the dairies. This duality is significant because attemptsby a paper company to supply a superior container by altering the blankconfiguration are thus constrained, i.e. a paper company cannot supply ablank which has been modified to the extent that the form, fill and sealmachine will not accept it. Thus, any alteration made in the blankconfiguration must be such that it will not affect the ability of themachine to form a container from the blank.

In general, the problem of supplying blanks to a dairy for use inpackaging milk has been resolved since a fully acceptable containerblank for packaging milk has been designed and is known to the priorart. However, a very significant problem arises when a dairy elects topackage and sell a liquid product other than milk. A similar problemarises when a company other than a dairy desires to use paperboard milkcarton type containers to package liquids other than milk. The problemswhich arise under these circumstances are significant and often quitedifficult to solve. The problem is significant because such companiescan often achieve substantial economies if paperboard containers can beused. However, the difficulty arises because in order to achieve theseeconomies form, fill and seal machines of the type used by dairies mustbe employed which, in turn again places a limitation upon themodifications which can be made by a paper company to the blank whichthey are supplying. In other words, the same container which is used tosuccessfully package milk might not be successfully used to packageother liquids. Examples of such other liquids, which may be referred toas penetrative liquids, are cooking oils and diet soft drink syrups.Liquids of this latter type, when packaged in milk carton typecontainers, frequently leak through the bottom closure of the containernotwithstanding the fact that the same bottom closure and container maybe used to successfully package milk. Indeed, an index of the difficultyof packaging liquids such as soft drink syrups is the fact that milkcarton type containers are often provided with an interior metal foillaminate when such containers are used to package soft drink syrups. Acontainer and container blank employing such a construction is disclosedin US. Pat. No. 3,365,111 which is incorporated herein by reference.

The invention disclosed herein comprises the combination of athermoplastic coated paperboard blank with an improved bottom closure. Ablank embodying the instant invention may be formed into a container ona standard form, fill and seal machine which is either unmodified oronly slightly modified depending upon the particular embodiment of theinvention which is used. Moreover, the container resulting from erectinga blank which embodies this invention (and which may also include aninterior metal foil laminate) may be used to successfully packagepenetrative liquids such as soft drink diet syrups.

2. Prior Art Referring to the drawings, FIG. 1 shows the lower half of apaperboard blank of the type known to the prior art and which may beerected to form a container for packaging milk. The upper part of theblank 12 shown in HO. 1 has been omitted since that part of the blank isknown to the prior art and does not particularly pertain to the instantinvention.

Referring to FIG. 1, it will be seen that the blank shown therein iscomprised of two major portions, i.e. a body forming portion 13 and abottom forming portion 14. The body forming portion 13 is comprised offour side wall panels 16, 17, 18 and 19, each having an equal width andforming the side walls of the erected container. The side walls 16, 17,18 and 19 are connected by longitudinal fold lines 67, 78 and 89respectively. The bottom forming portion 14 is comprised of four flaps16a, 17a, 18a and 19a. The aforementioned bottom forming flaps areconnected to the side panels by transverse fold lines 26, 27, 28 and 29respectively. Additionally, the four bottom flaps 160, I70, l8a and 19aare connected to each other by longitudinal fold lines 67, 78 and 89respectively, i.e. the longitudinal fold lines which interconnect thebottom forming flaps are extensions of the fold lines which interconnectthe side wall panels.

Generally, blanks of the type shown in FIG. 1 are provided with aso-called manufacturer joint which is foldably connected to one of theside walls, eg 16. When the blank 12 is formed into a tube, themanufacturers joint is typically heated by an exposed flame and is thenoverlappingly bonded to the interior surface of the side wall panel 19adjacent to its longitudinal edge 21.

Referring to bottom forming portion 14, it may be noted that certain ofthe bottom forming flaps which form this portion have a degree ofsymmetry. For example, referring to the bottom forming flaps 16a and18a, which may be defined as gusset forming flaps, it may be noted thatthese flaps are spaced apart by the flap 17a but are otherwisesymmetrical. Thus, their transverse edges 46a, 46b and 48a, 48b aretransversely aligned. Additionally, each of the gusset forming flaps isprovided with two diagonally disposed score lines which definesub-panels. For example, referring to flap 160, the diagonal score lines31, 32 define sub-panels 16b, 16c and 16d. Similarly, diagonal scorelines 33, 34 on the flap 18a define sub-panels 18b, I86 and 18d.

Flap 19a may be referred to as a tuck-in flap and flap 170 may bereferred to as a cover flap. It may be noted that in the prior artconstruction shown in FIG. 1, the transverse edge 49 of the tuck-in flap19a and the transverse edge 47 of the cover flap 170 are substantiallyaligned.

When a blank of the type shown in FIG. 1 is to be erected to form acontainer, the blank is first formed into a tube as heretoforedescribed. Thereafter, the gusset forming flaps 16a and 180 are urgeddownwardly into the containerv As a result of this action, thetriangular sub-panels 16b and 18b may be moved into a generallyhorizontal position. As a result of this action, the subpanels 16c, l6dand 18c, l8d are folded back to horizontally overlie the sub-panels 16b,18b respectively. Thus, a so-called gusset or triangular configurationis formed. The resulting triangular panels or gusset panels have an apexof the gusset points 40, 41.

Because all of the bottom forming flaps are foldably interconnected, thetuck-in flap 19a and the cover flap 170 will be moved into a horizontalposition when the gusset forming flaps 16a, l8a are positioned asdescribed above. More particularly, it may be noted that thelongitudinal length of the tuck-in flap 19a and the cover flap 17a isgreater than the longitudinal length of the gusset forming flaps. Withregard to these dimensions, a number of factors should be pointed out.First, it may be noted that the adjacent transverse score lines areslightly displaced from each other. Thus, score lines 26, 28 are alignedwith each other but are slightly longitudinally displaced from thealigned score lines 27, 29. This slight displacement of the longitudinalscore lines is provided to insure that when the bottom is formed thereis relatively no interference. Thus, the transverse score linesassociated with the gusset forming flaps 16a, 18a are displaced slightlyabove the transverse score lines associated with the flaps 17a and 19abecause the gusset forming flaps will be folded first and the flaps 17aand 19a will overlie the gusset forming flaps.

With further regard to the dimensions of the bottom forming flaps, itshould be noted that containers of the type erected from a blank shownin FIG. 1 are generally square. Thus, the longitudinal height of thegusset forming flaps is generally equal to or slightly less than thewidth of the side wall panels so as to insure that when the gussetforming flaps are positioned within the container, the gusset points 40,41 are almost touching.

Returning to a consideration of the manner in which the bottom formingportion of the blank 12 is erected, after the gusset forming flaps havebeen positioned horizontally within the container, the tuck-in flap 19ais horizontally positioned. Similarly, the cover flap 17a is alsohorizontally positioned so as to overlie the tuck-in flap 19a. Thus, itwill be appreciated that the word tuck-in accurately describes the flap190 since, when the bottom is formed, the edge 49 of the tuck-in flap19a is, in fact, tucked in between the cover flap 17a and the sub-panels16c, 16d and 18c, 18d.

Referring to FIG. 2, there is shown a view which illustrates a containerbottom which would result from erecting the blank shown in FIG. 1. Moreparticularly, the view shown in FIG. 2 is that which would appear if oneviewed the resulting bottom closure looking down into the tube or openended container. The resulting construction shown in FIG. 2 exemplifiesthe prior art and is representative of the bottom construction used onmost paperboard milk cartons. Thus, it is instructive to consider thisconstruction in some detail in order to obtain an understanding as towhy this construction is deficient when one attempts to package certainliquids.

Considering the construction shown in FIG. 2, it may be noted that thegusset points 40, 41, disposed in the center of the container, arealmost touching and define what might be referred to as a central axis.As previously indicated, the tuck-in flap 19a is disposed between thegusset forming flaps and the cover flap 17a. This is particularlyevident in FIG. 2 where it may be noted that the edge 49 of the tuck-inflap 19a is clearly visible.

Another exposed edge which is clearly visible is the edge 20 associatedwith the manufacturers joint 15.

As previously indicated, when the gusset forming flaps 16a and 180 arefolded into a horizontal position, their respective sub-panels 16c, 16dand 18c, 18d are folded back so as to form the gusset points 40, 41. Asa result of this fold back action, the transverse edges associated withthe gusset forming flaps are ultimately disposed in a channel formingrelation. Thus, referring to FIG. 2, it may be seen that the transverseedges 46a and 46b associated with the gusset forming flap are disposedparallel to each other and underneath the gusset panel 16b. Similarly,the transverse edges 48a and 48b associated with the gusset forming flap180 are disposed parallel to each other and underneath the gusset panel18b.

Having described in considerable detail the prior art bottomconfiguration shown in FIG. 2, the deficiencies thereof and the mannerin which these deficiencies arise may be clearly understood.Fundamentally, it has been discovered that all of these deficiencies arein the nature of leakage paths and appear to arise when there is adiscontinuity between overlapping flaps or panels. Thus, it is believedthat such discontinuities essentially form a channel through whichleakage may occur. For example, referring to FIG. 2, when a bottom ofthe type shown therein is formed, a leakage channel is oftensimultaneously created along the exposed edge 49 of the tuck-in flap19a. Liquid entrance to this leakage channel would occur at theintersection of the exposed edge 49 and the fold lines 32, 33. Themanner in which this channel is formed may be appreciated by referringto FIG. 3 wherein the interrelation between various overlying panels andflaps is shown. Thus, in FIG. 3, it will be seen that the transverseedge of the tuck-in flap 190 causes a channel to form which is shown incross section at 60 and may be referred to as the tuck-in flap channel.

Referring again to FIG. 2, the arrows 61 generally indicate paths ofleakage along the exposed edge 49. The arrows 61 terminate at the edgesof the container where the final leakage may occur. In an effort toblock the leakage path formed by the exposed edge 49, the prior art hasresorted to what are referred to as stakes. Briefly, stakes areindentations (22, 23 FIG. 2) formed in the bottom of container blanksperpendicularly across a leakage path. The stake or indentation isformed by providing a small, correspondingly shaped protuberance on thepressure pad on the form, fill and seal machine. The theory of stakingis to provide, during the formation of the bottom, a zone which issubjected to high pressure and, thus, it is hoped the leakage channelwill be blocked. While the use of stake points has been successful inpreventing the leakage of milk, the same procedure has been relativelyunsuccessful when attempts have been made to use milk carton typecontainers to package liquids such as diet soft drink syrups.

Another leakage channel which is commonly formed and difficult to sealmay be referred to as the gusset channel and is formed by the transverseedges of the gusset forming flaps. Thus, referring to the sectional viewof FIG. 4, it may be seen that a gusset channel, shown in cross sectionat 61, is formed between the two sub-panels 18d, 180, the gusset panel18b and the tuckin flap 19a. Entrance to the gusset channel is generallyafforded at the gusset points 40, 41.

In general, attempts to package penetrative liquids in containers whichhave a bottom of the type shown in FIG. 2 have been unsuccessful becauseleakage occurred along either the channel 60 formed by the exposed edge49 or the gusset channel 61. As will hereinafter be described, theinstant invention prevents leakage along these channels.

Although the prior art has recognized the need to provide a leak proofbottom, an effective and economical solution to this problem has notheretofore been found when such containers are used to packagepenetrative liquids such as diet soft drink syrup. The art has attemptedto' provide a leak proof bottom by overcoating the entire bottom of thecontainer. For example, one such prior art approach contemplatesspraying the entire bottom interior of a carton with wax or athermoplastic material after it is erected. Of course, such an approachrequires a substantial addition to and modification of the formingmachine and, additionally, consumes a considerable quantity of coatingmaterial. U.S. Pat. No. 3,365,111 discloses such a formed containerwherein the bottom exterior is overcoated with a film. A similarovercoating, in the nature of an increased coating of the bottom panels,is disclosed in U.S. Pat. No. 3,421,678. Apparently, the prior artresorted to the overcoating approach because of the assumed difficultyor impossibility of selectively applying a bead or globule ofthermoplastic coating material at the prime location of the leak formingcreases" described in U.S. Pat. No. 3,421,678.

In summary, the two leakage channels associated with a bottom closure ofthe type most commonly used by the prior art have been described. Theinvention disclosed herein and hereinafter described seals these leakagechannels.

SUMMARY OF THE INVENTION In combination with a thermoplastic coatedpaperboard blank of the type commonly used to form milk containers, animproved bottom forming portion is provided. In accordance with theimprovement, the center portion of the transverse edge of the tuck-inflap is transversely aligned with the transverse edges of the gussetforming flaps. Additionally, thermoplastic film patches are provided onthe blank which seal the two leakage channels described above when theblank is erected.

In the preferred embodiment of the invention, the thermoplastic filmpatches are bonded to the paperboard blank on the interior side thereofand overlying the gusset points.

The thermoplastic film patches preferably have a melt index in the rangeof 3.0 to 300.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a view of a paperboard blank knownto the prior art.

FIG. 2 is a plan view of a container bottom of the type resulting fromerecting the blank of FIG. 1.

FIG. 3 is a fragmentary, sectional view taken along the section lines3--3 of FIG. 2.

FIG. 4 is a fragmentary, sectional view taken along the section lines4-4 of FIG. 2.

FIG. 5 is a view illustrating an embodiment of the instant invention.

FIG. 6 is a plan view of a container bottom of the type resulting fromerecting the blank of FIG. 5.

FIGS. 7 and 8 are plan views of a container bottom and illustrate astructural requirement of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 5, apaperboard blank 12' is shown and represents one embodiment of myinvention. As may be noted, a major portion of the blank 12' shown inFIG. 5 is substantially identical to the blank 12 of FIG. I. Thus, tothe extent that these two blanks are the same, the same referencenumbers have been employed.

The first structural difference between the blank 12' of FIG. and theblank 12 of FIG. 1 comprises a notch or cutout 80 in the tuck-in flap19a. The purpose of the cut-out 80 is to alter the structure of thetuck-in flap 190 such that the center portion of the transverse edgethereof is aligned with the transverse edges of the gusset forming flaps16a and 180. Thus, it will be seen that there is provided a transverseedge 81 which is centrally located on the flap 19a and aligned with thetransverse edges 46a, 46b and 48a, 48b of the gusset forming flaps.

The second structural difference between the prior art blank shown inFIG. I and the embodiment shown in FIG. 5 relates to the addition ofthermoplastic film patches. More particularly, referring to FIG. 5, itmay be noted that two patches 90 and 91 have been provided. The patches90, 91 are thermoplastic material, e.g. patches of thermoplastic film.The patches are bonded, by heat sealing, preferably to the interiorsurface of the blank 12 and are disposed on each of the gusset formingflaps 16a, 18a in a position such that they cover the gusset points and,extend slightly beyond the transverse edges of the associated gussetforming flaps. The significance of providing such thermoplastic filmpatches (the patches 90 and 91) in combination with a tuck-in flaphaving the center portion of its transverse edge aligned with thetransverse edges of the gusset forming flaps will now be described.

Referring to FIG. 6, there is shown a plan view of the interior bottomof a container formed from a blank of the type shown in FIG. 5.Considering in detail the structure shown in FIG. 6, it may initially benoted that the effect of providing the cut-out 80 as previouslydescribed is to produce a bottom closure wherein the edge of the tuck-inflap 190 which is exposed to the interior of the container (i.e. exposedto the liquid packaged therein) is aligned with and disposed immediatelybeneath the gusset points. Thus, in terms of the leakage channelsheretofore described, the effect of this construction is to insure thatthe gusset channels and at least a portion of the tuck-in flap channelare coincidently aligned. Having achieved this result, the thermoplasticfilm patches 90, 91 may now be used to uniquely cooperate so as to sealthese leakage channels. Thus, when the container blank 12' of FIG. 5 isformed and subjected to a heat sealing step, the thermoplastic patches90, 91 which are touching or substantially abutting, are melted andlocally flow so as to cover and adhere to not only the gusset points towhich they were attached, but, as well, to the adjacent center portionof the tuck-in flap 19a and the cover flap 170. As a result, the gussetpoints are sealed and, simultaneously, the melted patches form a seal 99blocking the entrance to the tuck-in flap channel. Thus, it will beappreciated that, by providing the patches 90, 91 and providing atuck-in flap having the center portion of its transverse edge alignedwith the transverse edges of the gusset forming flaps, a blank isprovided which, when erected, has an improved bottom closure, Le. abottom closure wherein the two major sources of leaks have beeneliminated.

Since the purpose of the thermoplastic film patches is to insure asealing action of the type previously described, it will be appreciatedthat such a sealing means can be provided, on a paperboard blank, inpositions other than the positions of the patches 90, 91 as shown inFIG. 5. Thus, although the construction shown in FIG. 5 and previouslydescribed represents one of the preferred embodiments of my invention,an essentially acceptable erected container can also be obtained if thethermoplastic film patches are in the form of a single patch disposedupon and heat-sealed to the tuck-in flap 19a at the center of the flapand adjacent the transverse edge thereof. Thus, in FIG. 5 a dotted linerepresentation of a patch 86 is shown as being disposed upon theinterior surface of the tuck-in flap 19a. Once again, when the containeris erected and sealed, the patch 86 will seal both the gusset points andthe entrance to the tuck-in flap channel.

Another configuration which will result in an essentially acceptablecontainer bottom involves the provision of a thermoplastic patch on theinterior of the surface of the cover flap 17a. Thus, in FIG. 5, such apatch is shown by the dotted line representation 87.

With regard to the thermoplastic patches described above, thethermoplastic material selected must meet certain criteria. For example,the material which comprises the thermoplastic patch must be such thatit will, upon melting and rehardening, adhere to the thermoplasticcoating on the paperboard blank. Thus, if the blank is coated withpolyethylene, the thermoplastic material used for the patch must satisfythis requirement with respect to polyethylene. Another requirement whichsuch thermoplastic material must satisfy relates to the so-called meltindex. Essentially, the melt index is a measure of the flowability orviscosity of a thermoplastic at an elevated temperature. In order for athermoplastic material to perform satisfactorily as a thermoplasticgusset point sealing means, the thermoplastic must have a degree offlowability at the heat sealing temperatures which are encountered inorder to insure that the heated thermoplastic material will flow ontoadjacent flaps and will flow into and seal the entrance to the leakagechannels. However, the viscosity of the heated thermoplastic cannot beso low that the heated thermoplastic will be unduly dissipated byflowing over too large an area. Experiments conducted upon the occasionof this invention have determined that a thermoplastic with a melt indexin the range of, approximately, 3.0 to 300 is acceptable. Examples of anacceptable thermoplastic are DuPonts Surlyn AD 8109 and polyethylene. Ifa thermoplastic is used which has a melt index in the range of 3.0 to300, an acceptable patch may be approximately 0.75 inches square and0.075 thick.

With general regard to the embodiment of this invention shown in FIG. 5,it has been heretofore pointed out that one element of the inventionrelates to the provision of a cut-out 80. From a structural point ofview, the cut-out must provide a blank construction which satisfies twocriteria. First, the center portion of the transverse edge of thetuck-in flap at least must be substantially aligned with the transverseedge of the gusset forming flaps so that when a container is formed, thegusset points are substantially aligned with the exposed edge of thetuck-in flap. Second, the remainder of the exposed edges of the tuck-inflap must be so disposed as to underlie the gusset forming flaps whenthe blank is erected. The second requirement must be satisfied to insurethat the only entrances to the tuck-in flap channel are adjacent to thegusset points. Thus, the edges of the tuck-in flap may be disposed asshown in FIG. 7 but not as shown in FIG. 8 wherein the remainder of theedges of the tuck-in flap do not all underlie the gusset flaps, e.g. asat l] and 102. An acceptable alternative construction would be totransversely cut the tuck-in flap so that it was longitudinallyco-extensive with the gusset flaps as suggested by the dotted linerepresentation 104, 105 in FIG. 5.

As previously indicated, structural changes made to a paperboard blankof the type shown in FIG. may necessitate minor modifications to themachine which forms such a blank into a container. in this regard, thoseskilled in the art will appreciate that it is common to modify theso-called pressure pad of a form, fill and seal machine in order toinsure that the pressure pad conforms to the exterior of the bottom ofthe container. Thus, when a container blank of the type shown in FIG. 5,ie a container blank having a cut-out, is erected on a form, fill andseal machine, it has been found to be beneficial to add a boss to theface of the pressure pad in order to occupy the slight indentation whichresults from the absence of the cut-out material. This preferred machinemodification may be rapidly accom plished, requires no significantalteration of the machine and involves a negligible material cost.

Reflecting upon the above description of the instant invention, it willbe evident that, in general, the improvement which characterizes theinvention includes two separate and distinct structural changes oradditions to prior art blanks and the structural changes cooperate toprevent leakage through the gusset channels and the tuck-in flapchannels. Thus, the invention generally contemplates providing, incombination with a paperboard blank, a bottom forming portion wherein atleast the center portion of the transverse edge of the tuck-in flap issubstantially aligned with the transverse edges of the gusset formingflaps and the remainder of the exposed transverse edges of the tuck-inflap are disposed to underlie the gusset forming flaps when the blank iserected. Additionally, the blank is provided with at least onethermoplastic film patch which is disposed on the container such thatwhen the container is erected and heat sealed, the thermoplastic filmpatch will seal the gusset points and the substantially coincidentlyaligned tuck-in flap channels. Further, it is important to note that thethermoplastic patch or patches must be shown disposed upon theirrespective bottom forming flaps such that the lower transverse edge ofthe patch extends beyond the transverse edges of the gusset formingflaps. Such a positioning of the thermoplastic patches is importantbecause of the mechanism by which sealing occurs. Thus, with thethermoplastic patch or patches disposed in this manner, when the bottomof the container is formed, the portion of the patch which extendsbeyond the edge of the gusset flaps will overlie and be disposed in thecenter of the container. In this manner, when the patch melts, theentrances to the gusset channel and the tuck-in flap channel will besealed. Referring to FIG. 5, it may clearly be seen that each of thefour patches shown therein has a portion which extends beyond thetransverse terminal edge of the gusset forming flaps.

In the context of this description of this invention, it should beunderstood that the phrases coincidently aligned or transversely alignedrefer to an alignment of at least the center portion of the transverseedge of the flap 19a with the gusset points such that when thethermoplastic patches melt, the gusset points and the tuckin flapchannels are sealed.

in summary, a number of embodiments of the instant invention havehereinbefore been disclosed and described. However, it will beappreciated that other embodiments may be apparent to those skilled inthe art which are nevertheless within the scope of the invention as setforth in the claims appended hereto.

We claim:

1. In combination with a thermoplastic coated paperboard blank adaptedto be erected to form a square, heat sealed container, said blank havinga body forming portion and a bottom forming portion, said bottom formingportion including two spaced apart gusset forming flaps havingsubstantially aligned transverse edges and forming gusset points whensaid blank is erected, a cover flap foldably connected by a longitudinalfold line to at least one of said gusset forming flaps, and a tuck-inflap foldably connected by a longitudinal fold line to at least one ofsaid gusset forming flaps, the improvement which comprises:

a. at least the center portion of the transverse edge of said tuck-inflap being substantially aligned with the transverse edges of saidgusset forming flaps and the remainder of the edges of said tuck-in flapdisposed to entirely underlie said gusset forming panels when said blankis erected; and

b. a thermoplastic film patch bonded to at least one of said flapsadjacent to the center of the transverse edge thereof and extendingbeyond the transverse edge of said gusset forming flaps whereby, whensaid blank is erected and heat sealed to form a container, both saidgusset points and the center portion of the transverse edge of saidtuck-in flap are sealed by said thermoplastic film patch.

2. The blank of claim 1 wherein a thermoplastic film patch is bonded toeach of said gusset forming flaps and overlies said gusset points.

3. The blank of claim 2 wherein said blank is coated with polyethyleneand said thermoplastic film patch is polyethylene.

4. The blank of claim 2 wherein said tuck-in flap is notched.

5. The blank of claim 4 wherein said notch has parallel, longitudinalside edges.

6. The blank of claim 5 wherein said thermoplastic patch has a meltindex in the range of approximately 3.0 to 300.

7. The blank of claim 4 wherein said notch has divergent side edges.

8. The blank of claim 7 wherein said thermoplastic patch has a meltindex in the range of approximately 3.0 to 300.

9. The blank of claim 2 wherein said thermoplastic film patches arebonded to the interior surface of said gusset forming flaps.

10. The blank of claim 1 wherein said thermoplastic film patch is bondedto the interior surface of said tuckin flap and overlies the centerportion of said tuck-in flap adjacent to the transverse edge thereof.

11. In combination with a thermoplastic coated paperboard blank adaptedto be erected to form a heat sealed container, said blank having a bodyforming portion and a bottom forming portion, said bottom formingportion including two spaced apart gusset forming fiaps havingsubstantially aligned transverse edges and forming gusset points whensaid blank is erected, a cover flap foldably connected by a longitudinalfold line to at least one of said gusset forming flaps, and a respectiveone of said gusset forming flaps so as to overlie said gusset points andeach of said patches extending beyond the transverse edge of said gussetforming flaps whereby, when said blank is erected and heat sealed toform a container, both said gusset points and the center portion of thetransverse edge of said tuck-in flap are sealed by said thermoplasticfilm patch.

1. In combination with a thermoplastic coated paperboard blank adaptedto be erected to form a square, heat sealed container, said blank havinga body forming portion and a bottom forming portion, said bottom formingportion including two spaced apart gusset forming flaps havingsubstantially aligned transverse edges and forming gusset points whensaid blank is erected, a cover flap foldably connected by a longitudinalfold line to at least one of said gusset forming flaps, and a tuck-inflap foldably connected by a longitudinal fold line to at least one ofsaid gusset forming flaps, the improvement which comprises: a. at leastthe center portion of the transverse edge of said tuck-in flap beingsubstantially aligned with the transverse edges of said gusset formingflaps and the remainder of the edges of said tuck-in flap disposed toentirely underlie said gusset forming panels when said blank is erected;and b. a thermoplastic film patch bonded to at least one of said flapsadjacent to the center of the transverse edge thereof and extendingbeyond the transverse edge of said gusset forming flaps whereby, whensaid blank is erected and heat sealed to form a container, both saidgusset points and the center portion of the transverse edge of saidtuck-in flap are sealed by said thermoplastic film patch.
 2. The blankof claim 1 wherein a thermoplastic film patch is bonded to each of saidgusset forming flaps and overlies said gusset points.
 3. The blank ofclaim 2 wherein said blank is coated with polyethylene and saidthermoplastic film patch is polyethylene.
 4. The blank of claim 2wherein said tuck-in flap is notched.
 5. The blank of claim 4 whereinsaid notch has parallel, longitudinal side edges.
 6. The blank of claim5 wherein said thermoplastic patch has a melt index in the range ofapproximately 3.0 to
 300. 7. The blank of claim 4 wherein said notch hasdivergent side edges.
 8. The blank of claim 7 wherein said thermoplasticpatch has a melt index in the range of approximately 3.0 to
 300. 9. Theblank of claim 2 wherein said thermoplastic film patches are bonded tothe interior surface of said gusset forming flaps.
 10. The blank ofclaim 1 wherein said thermoplastic film patch is bonded to the interiorsurface of said tuck-in flap and overlies the center portion of saidtuck-in flap adjacent to the transverse edge thereof.
 11. IN combinationwith a thermoplastic coated paperboard blank adapted to be erected toform a heat sealed container, said blank having a body forming portionand a bottom forming portion, said bottom forming portion including twospaced apart gusset forming flaps having substantially alignedtransverse edges and forming gusset points when said blank is erected, acover flap foldably connected by a longitudinal fold line to at leastone of said gusset forming flaps, and a tuck-in flap foldably connectedby a longitudinal fold line to at least one of said gusset formingflaps, the improvement which comprises: a. at least the center portionof the transverse edge of said tuck-in flap being cut so as to bealigned with said gusset points when said carton is formed and theremainder of the edges of said tuck-in flap disposed to entirelyunderlie said gusset forming flaps when said blank is erected; and b.two thermoplastic film patches; each bonded to a respective one of saidgusset forming flaps so as to overlie said gusset points and each ofsaid patches extending beyond the transverse edge of said gusset formingflaps whereby, when said blank is erected and heat sealed to form acontainer, both said gusset points and the center portion of thetransverse edge of said tuck-in flap are sealed by said thermoplasticfilm patch.